Fix inheritence hierarchy for the API interfaces under the Interfaces\* namespace.
PINQ hierarchy rules:
 - ITraversable: the root interface
 - IQueryable extends ITraversable: with abstracted query provider
 - ICollection extends ITraversable: with mutability aspect
 - IRepository extends IQueryable, ICollection: with abstracted query provider and mutability aspect.

All can be passed where an ITraversable is requried.
An IRepository can be passed where an ICollection is required.
An IRepository can be passed where an IQueryable is required.